Friction element and method of making the same



Patented Mar. 17, 193

PATENT OFFICE mIc'moN ELEMENT AND ism'r'non F MAKING THE SAME JamesDriscoll, Plainfield, and Donald S. Bruce,

Some'rville, N. J., assignors to Johns -Manville Corporation, New NewYork No Drawing.

York, N. Y., a corporation of Application October 28, 1932, Serial No.640,134

Claims. (01. 106-23) This invention relates to an impregnated article ofmanufacture, particularly a friction element,'and to the method ofmaking the same.

A conventional friction material or element adapted for use as brakelining 'or clutch facing, of automobiles, for example, comprisesasbestos fibers and a friction compound, The friction compound may beone containing a large pro-. portion. of rubber, pitch, or othersemiplastic binder of suitable properties.

It is an object of the present inventionto provide a friction materialthat has an increased coefiicient of friction, increased resistance towear, or increased resistance to change in properties at moderatelyelevated temperatures, as compared to conventional brake lining.

The invention comprises the novel features hereinafter'claimed ordescribed and, especially,

a product comprising reenforcing fibers, a waterinsoluble,heat-resistant, inorganic substance precipitated in intimate associationwith the said fibers, and a friction compound adhering the whole into anarticle adapted for use as a friction element. The invention comprisesalso the method of manufacturing the improved product which includesprecipitating in situ a heat-resistant, inorganic substance, in intimateassociation with reenforcing fibers, then applying friction compound tothe thus treated fibers, and forming a unitary product.

The invention is illustrated by the following specific example of themaking of-a product in which asbestos yarn is intimately associated withcalcium silicate, precipitated withir fand between the several units ofyarn and enmeshed in the fibers therein; the thus treated yarn isprovided with a coating or impregnation of a rubber fric-' tioncompound, the coated or impregnated yarn is compressed and densifiedinto an article of desired shape, and the rubber therein is hardened byvulcanization.' I v There is provided a supply of asbestos yarn that ispreferably wire-inserted, that is, wire-reenforced. A yarn that has beenused to advantage is scrap asbestos yarn that has been cut and/or.shredded into short lengths averaging, say, approximately 1 to 3 incheslong. The short lengths of asbestos yarn are then immersed inorthoroughly wetted by an aqueous mixture, actually a suspension, ofhydrated lime containing suitablylO to 50 parts by weight of lime, say,25 parts, to '75 parts by weight of water. The mixture is made intimate,as'by agitation, so that the fine particles of hydrated. lime becomeintween the various fibers comprising the individual strands of yarn.The yarn is an especially desirable form of unit of asbestos in thistreatment, since the yarn does not collapse into large masses when Wet."i 5 The yarn thus associated with the lime, either after drying at anelevated temperature, as, for example, at approximately 200 F., or,without drying, is treated with a soluble silicate. For the treatmentthere has been used to advantage a commercial solutionof sodium silicatein water, of a density of approximately 20.IBaumt-a. This treatmentcauses the conversion of lime into a precipitate of calcium silicate.Because the lime was initially lodged within and around the fibers inthe yarn, the precipitate formed is intimately associated with anddistributed throughout the fibers composing the yarn. The precip itatedmaterial is in finely divided form.

The silicated yarn thus formed may be subjected to washing with water,in any convenient and satisfactory manner, to remove soluble materialspresent. This washing is designed to remove unused sodium silicate, ifany is present, as well as the soluble by-product of the interactionofthe lime with the silicate.

The washed product is then subjected to drying, suitably atan elevatedtemperature, say, at approximately 200 F. The thus treated yarn is thenimpregnated with rubber friction or binder compound. The rubber compoundmay consist of ingredients which are conventional in brake Total Thecompound is applied, advantageously, in the form of a rubber cement,that is, in solution in a volatile solvent. The rubber compound is dis-50 tributed thoroughly over the various units of dry silicated yarn andthe volatile solvent is evaporated. The thus rubberized yarn is placed,in suitable quantity, into a shaping and vulcanizing die and iscompressed and densified in the die, to 55- establish the shape desiredin the finished article. The rubber binder in this shaped article isvulcanized, as, for example, by steam heat applied to the shaping die,supplemented, suitably, by additional vulcanization in a .steam -heatedoven after the shaped and partly vulcanized material isremoved from thedie.

The product so made, as compared to brake lining including asbestos yarnand rubber binder compound but not including the insoluble silicateassociated with the fibers, has a greatly increased coefficient offriction, decreased rate of wear, and is adapted for use at highertemperatures, that is, under more severe conditions of braking.

In order to minimize the tendency of the brake lining to score the brakedrum against which it is applied, there may be incorporated with therubber binder compound, in a process of manufacture that is otherwisesimilar to the one describedabove, an anti-scoring agent, that is, amaterial adapted to modify slightly the hardness of the product. Thus,there has been used to advantage a resinous polychlordiphenyl that meltsat about 158 F. to a viscous liquor and is known as arachlor, in theproportion of about 2 parts of the anti-scoring agent for 100 parts byweight of rubber in the compound. In general, the anti-scoring agentshould be a latent softener which becomes an effective lubricant onlywhen the temperature exceeds a certain point, as under conditions whichmake the brake drum relatively susceptible to scoring. High melting,lubricating, relatively non-volatile, inert substances may be used.

Various alternatives may be used in place of the materials describedabove.

In general, the material used as the friction mi mum or binder may beone that is commonly used in friction materials and is, advantageously,semiplastic or plastic initially and semirigid in the final product. Itmay also be resilient. Preferably, the binder is one that is adapted tobe hardened after being incorporated into the fibrous material. Thus,there may be used a drying oil, thatis, one adapted to be hardened bypolymerization and/or oxidation, such as China-wood oil, linseed, orperilla oil. Such an oil, when used, is hardened in the shaped articleby being maintained at an elevated temperature in the presence of air.Another binder that may be used is a resinous material, say, aphenolaldehyde condensation product. Another that may be used when theasbestos is fabricated, into a woven fabric, for example, is asphalt orother bituminous material.

The term rubber as used 'herein is intended to include natural,reclaimed, and/or synthetic rubber. A synthetic rubber that may be usedis polymerized chloro-2-butadiene-1,3, of empirical formula,CHzzCcLCHzcH-z, and made as deused in association with a largerproportion of asbestos fibers, say, approximately 1 part by weight ofcotton fibers fabricated with 4 parts of asbestos. In cases whereheat-resistance is not required, cotton or wool fibers may be usedalone, say in the form of short lengths of yarn. However, asbestosfibers are particularly desirable; because of the structure of thevisible fibers which are composed individually ofbundles of microscopic,elongated crystals, the fibers are adapted to be penetrated at theirfrayed portions, at least, in the treatment described above, and,thereby, to become veryintimately 8550! ciated with the precipitateproduced.

The fibers may be in the form of short lengths of yarn, as stated, or ofa fabric, either felted or woven.

In making aproduct containing a felted fabric, lime, for example, issuspended with asbestos fibers and water in a beaterof paper mill typeand the mixture felted into a paper on a paper machine, The resultingpaper is then treated with a solution of sodium silicate, washed withwater, dried, and impregnated with a solution of a binder, such as adrying oil, a bituminous material, or a resin dissolved in a volatilesolvent. Volatile material added in the impregnation is then evaporatedand the impregnated product is subjected to conventional treatment forhardening the binder therein and for compressing, if desired.

In making a product containing a woven fabric, reenforced asbestos yarnmaybe immersed in an aqueous suspension of hydrated lime, for example,and then woven into a fabric, the fabric treated with sodium silicatesolution, washed to remove soluble substance present after the treatmentor not washed, dried, impregnated with rubber or other binder and thebinder therein hardened. Or, thefabric may be woven from untreated yarnand the woven fabric treated with an aqueous suspension of hydrated limeand then with a solution of sodium silicate, and finished as describedabove.

The water-insoluble, inorganic substance precipitated in intimateassociation with the fibers, maybe one that is heat-resistant,wear-resisting under friction, non-corrodible, finely divided inform,and durable under the conditions to which 4 cipitation in sitii,preferably there is lodged within the fibers, by means of an aqueoussuspension or-as-a dust, a compound of the type of lime, that is, arelatively insoluble compound of a metal adapted to produce aprecipitate with a selected compound of the type of a water-solublesilicate, as, for example, an alkali metal silicate phosphate, and thenapplying a water solution of the said'selected compound. The subsequentoperations may be performed as described-above.

- In order to preserve the semirigidity and/or resiliency of the finalproduct containing rubber binder compound or the like, the proportion ofheat-resistant inorganic precipitate in association with the flbers'therein should not be so large as to make a stone-like product andshould be, for example, less than 100 parts, say approximately 50 partsfor each 100 parts of the asbestos units (yarn or fabric).

It will be understood that silicated units of asbestos may be blendedwith untreated asbestos, in .various proportions, before the addition of'vention.

the binder compound. Also, he binder compound may be a mixture of two ormore conventional binders, such as those described above.

Thedetails that-have been given are for the purpose of illustration andnot restriction, and

many variations therefrom may be made Without departing from the spiritand scope of the in-= What we claim is:

i. A friction element comprising heat-resistant fibers, awater-insoluble, heat-resistant, inorganic substance precipitated inintimate association with the said fibers, and a friction compound, in-

1 eluding a binder and an admixed anti-scoring agent, adhering the wholeinto a unitary product,

the. anti-scoring agent being a high melting, 1761a,

tiveiy non-volatile solid adapted, at elevated temperatures of use'oithe friction element, to modi- 2y the hardness thereof and providelubrication and relatively insoluble compound oi a metal aoaaeeo adaptedto form a precipitate in situ when a solution of another selectedcompound is applied, applying to the treated fibers a solutioncontaining the said selected compound, whereby precipitation isproduced, washing to remove soluble materials present after theprecipitation,

drying the product, and then impregnating with a friction compound.

4. A friction element, adapted for automotive brake lining, comprising afibrous "material including the products of the interaction, in thepresence of water, of asbestos fibers, a relatively insoluble compoundof the type of lime, and

a compound of the type of a water-soluble silicate and a friction bindercompound adhering the said fibrous material into a unitary product, theproduct being substantially identical with that produced as described inclaimb.

5. In making an article of manufacture adapted for use as a frictionelement, the method which comprises incorporating an undissolved andrelatively insoluble compound, of the type of lime,

within a fibrous asbestos product, causing the said compound to reactwith a water-soluble substance, of the type of sodium silicate, adaptedto form within the said product a precipitate with the said compound,and then applying a friction compound to the said product andprecipitate contained therein.

' JAMES 'DRISCOLL.

1"" S. BRUCE.

